Sample Size Calculator

Compute the required sample size for two-proportion comparisons.

Comprehensive Guide: Sample Size Calculator

The Clinical Importance

Commencing a clinical study without a priori power analysis is unethical and scientifically invalid. Institutional Review Boards (IRBs) and ethics committees mandate a rigorous justification for the proposed sample size to ensure the study is neither underpowered (wasting resources) nor overpowered (exposing unnecessary patients to risks).

The Statistical Science

This calculator computes the exact sample size needed to detect a difference between two proportions. It utilizes standard Z-approximations for two-sided tests, factoring in your desired Alpha (typically 0.05 for 95% Confidence) and Beta (Power, typically 80% or 90%), delivering ethics-board-ready text.

Step-by-Step Instructions

  1. Step 1: Input the anticipated event rate (proportion) in Group 1.
  2. Step 2: Input the expected event rate in Group 2.
  3. Step 3: Select your desired Statistical Power and Alpha level.
  4. Step 4: Copy the auto-generated methodological justification text for your ethics application.